JP2006286468A - Spark plug for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug reducing a discharge voltage while securing smoking resistance. <P>SOLUTION: This spark plug 1 is equipped with a mounting fixture 2, an insulator 3, a center electrode 4, and an earthed electrode 5. The center electrode 4 has a barrel part 41 and a slender part 42, and their boundary part 43 is disposed on the further base end side than the tip part of the insulator 3. The earthed electrode 5 has a base material 51 to be earthed and a projecting part 52, and the projecting part has an inside edge 521 and an outside edge 522. Distances R1, R2 from the center axis M to the inside edge and the outside edge in the diameter direction, the radius R3 of the slender part, and the radius R4 of an axial hole satisfy 0.7×R3≤1.2×R4. The distance G1 between the center electrode and the inside edge, the distance G2 between the tip part 321 and the outside edge, the axial distance L between the slender part and the projecting part, the axial distance H between the boundary line and the end of the insulator satisfy L≤G1≤1.2×L, G2+H>G1, and G2/G1≤1.5. The projecting part is formed in a region of 120°or more around the center axis M. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug for an internal combustion engine used for automobiles, cogeneration, gas pumps, and the like.

  Conventionally, there is a spark plug for an internal combustion engine used as an ignition device in an internal combustion engine such as an automobile engine. As shown in FIG. 19, the spark plug 9 for an internal combustion engine includes an insulator 92, a center electrode 93 held by the insulator 92, and an attachment that holds the insulator 92 with the insulator tip 921 protruding. A ground electrode 95 that forms a spark discharge gap 91 between the metal fitting 94 and the tip of the center electrode 93 is provided.

  In the spark plug 9, there is a possibility that the insulation resistance between the center electrode 93 and the ground electrode 95 decreases due to carbon fouling in which carbon adheres to the surface of the insulator 92, resulting in a smoldering state. In view of this, an invention has been disclosed in which the shape of the tip of the center electrode 93 is devised in order to ensure smoldering resistance (see Patent Document 1).

  As shown in FIG. 19, the spark plug 9 according to the present invention includes a body portion 931, a center portion 93, and a narrow-diameter portion 932 that is disposed on the distal end side of the body portion 931 and is thinner than the body portion 931. In addition, the boundary portion 933 between the body portion 932 and the small diameter portion 931 is disposed on the proximal end side with respect to the insulator distal end portion 921.

  Thereby, at the time of smoldering, it becomes easy to make a spark discharge along the surface of the inner wall 924 of the shaft hole 923 of the insulator 92, and the carbon adhering to the insulator 92 can be burned out. In other words, in a state in which no smoldering occurs, a spark discharge A is generated between the protruding portion 952 of the ground electrode 95 and the small diameter portion 932 of the center electrode 93. At the time of smoldering, a spark discharge B is generated between the ground electrode 95 and the body 931 of the center electrode 93, and along the inner wall 924 of the shaft hole 923 of the insulator 92 as a path. Thereby, the carbon adhering to the inner wall 924 is burned away, and the smoldering is eliminated.

However, the conventional spark plug 9 has the following problems.
That is, in recent years, in an internal combustion engine such as an automobile engine, a direct injection engine and a high compression ratio engine have been developed to improve fuel efficiency. Since the direct injection engine directly injects fuel into the combustion chamber, it is difficult for the fuel to vaporize, and carbon is likely to adhere to the insulator, so that improvement in smoldering resistance is required.
Moreover, since the compression pressure becomes high in a high compression ratio engine, the discharge voltage at the time of ignition tends to be high. Since an increase in the discharge voltage causes a dielectric breakdown of the insulator, a reduction in the discharge voltage is required.

  In order to further exhibit the carbon burnout effect during smoldering, it is necessary to bring the edge 953 of the ground electrode 95 close to the inner wall 924 of the shaft hole 923 of the insulator 92 as shown in FIG. However, in this case, the edge 953 of the ground electrode 95 is moved away from the edge 934 of the small diameter portion 932 of the center electrode 93, which may increase the discharge voltage.

  On the other hand, as shown in FIG. 21, when the edge 953 of the ground electrode 95 is brought close to the edge 934 of the small diameter portion 932, the discharge voltage can be lowered, but the edge 953 of the protruding portion 952 of the ground electrode 95 The inner wall 924 of the 92 axial hole 923 is moved away. Therefore, at the time of smoldering, there is a problem that spark discharge (see symbol B in FIG. 19) between the ground electrode 95 and the inner wall 924 of the shaft hole 923 becomes difficult and the smoldering resistance may be lowered.

JP 2004-6250 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a spark plug for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.

The present invention provides a mounting bracket provided with a mounting screw portion on the outer periphery, an insulator held by the mounting bracket so that the tip of the insulator protrudes, and an axial hole formed in the insulator in the axial direction. A spark plug for an internal combustion engine, comprising: a center electrode that is formed; and a ground electrode that forms a spark discharge gap between the center electrode,
The center electrode has a trunk portion inserted into the shaft hole of the insulator, and a narrow-diameter portion disposed on the distal end side of the trunk portion and formed narrower than the trunk portion. The boundary part with the small diameter part is arranged on the base end side from the insulator tip part,
The ground electrode has a grounding base material fixed to the mounting bracket, and a protrusion that is attached to the grounding base material and disposed to face the center electrode,
The protrusion has an inner edge on the side close to the central axis of the small diameter portion of the center electrode and an outer edge on the far side.
When the radial distance from the central axis of the small diameter portion of the central electrode to the inner edge and the outer edge is R1, R2, the radius of the small diameter portion is R3, and the radius of the shaft hole is R4,
Satisfy 0.7 × R3 ≦ R1, 0.5 × R4 ≦ R2 ≦ 1.2 × R4,
G1 is the distance between the center electrode and the inner edge, G2 is the distance between the tip of the shaft hole of the insulator and the outer edge, and the small diameter portion of the center electrode and the ground electrode When the axial distance between the protrusions is L, and the axial distance between the boundary line and the insulator tip is H,
L ≦ G1 ≦ 1.2 × L, G2 + H> G1, G2 / G1 ≦ 1.5 are satisfied,
The projecting portion is a spark plug for an internal combustion engine characterized in that it is formed in an angle region of 120 ° or more around the central axis of the narrow-diameter portion (claim 1).

Next, the effects of the present invention will be described.
The protruding portion of the ground electrode has the inner edge and the outer edge. Therefore, during non-smoldering, it is easy to discharge between the inner edge and the small-diameter portion, and during smoldering, it is easy to discharge between the outer edge and the trunk portion via the insulator tip. That is, the inner edge can be brought closer to the narrow diameter portion of the center electrode, and the outer edge can be brought closer to the tip of the shaft hole of the insulator. Thereby, at the time of non-smoldering, it becomes easy to discharge between an inner edge and a small diameter part, and a discharge voltage can be reduced. During smoldering, it becomes easy to discharge between the outer edge, the inner wall of the shaft hole of the insulator, and the body portion of the center electrode. As a result, the carbon adhering to the inner wall of the shaft hole can be easily burned out, and the smoldering resistance can be improved.

  The radial distance R1 from the central axis of the small diameter portion of the center electrode to the inner edge and the radius R3 of the small diameter portion satisfy 0.7 × R3 ≦ R1. Further, a distance G1 between the center electrode and the inner edge and an axial distance L between the small diameter portion of the center electrode and the protruding portion of the ground electrode are L ≦ G1 ≦ 1. Satisfy 2 × L. Therefore, the space between the inner edge and the edge of the small diameter portion can be made close, and the discharge voltage can be kept low.

  Further, the radial distance R2 from the central axis of the small diameter portion of the center electrode to the outer edge and the radius R4 of the shaft hole satisfy 0.5 × R4 ≦ R2 ≦ 1.2 × R4. . Therefore, at the time of smoldering, it becomes easy to cause a spark discharge between the outer edge of the protrusion and the shaft hole of the insulator, and smoldering resistance can be ensured.

  Further, a distance G1 between the center electrode and the inner edge, a distance G2 between the tip end portion of the shaft hole and the outer edge of the insulator, and a distance between the boundary line and the tip end portion of the insulator. The axial distance H satisfies G2 + H> G1 and G2 / G1 ≦ 1.5. For this reason, spark discharge can be performed at a low discharge voltage between the small-diameter portion and the protruding portion at the normal time when the smoldering is not smoldering.

  Further, the protruding portion is formed in an angle region of 120 ° or more around the central axis of the small diameter portion. Therefore, the carbon adhering to the insulator can be burned over a wide range, and the smoldering resistance can be sufficiently secured.

  As described above, according to the present invention, it is possible to provide a spark plug for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.

In the present invention (Claim 1), the spark plug for the internal combustion engine can be used as ignition means for the internal combustion engine in, for example, an automobile, a cogeneration system, a gas pressure pump, and the like.
In the present specification, the side of the spark plug that is inserted into the combustion chamber of the internal combustion engine is the front end side, and the opposite side is the base end side. Further, “axial direction” means the axial direction of the spark plug unless otherwise specified, and “radial direction” means a direction orthogonal to the axial direction.

Further, a radial distance R1 from the central axis of the small diameter portion of the central electrode to the inner edge, a radial distance R2 from the central axis of the small diameter portion to the outer edge, a radius R3 of the small diameter portion, The radius R4 of the shaft hole is
It is preferable that 0.7 × R3 ≦ R2 and 0.5 × R4 ≦ R1 ≦ 1.2 × R4 are satisfied.
In this case, at the time of smoldering, spark discharge is easily generated between the inner edge and the insulator, and smoldering resistance can be further improved. Moreover, when not smoldering, it becomes easy to perform a spark discharge between the outer edge and the small diameter portion, and it is possible to reduce the discharge voltage and improve the ignitability.

Preferably, the protruding portion has a ring shape, the inner edge is formed on the inner peripheral side of the ring shape, and the outer edge is formed on the outer peripheral side of the ring shape. ).
In this case, it becomes easy to form the inner edge and the outer edge at appropriate positions in a wide range. Therefore, it is possible to easily ensure smoldering resistance and reduce the discharge voltage.

Further, it is preferable that two or more of the protrusions are disposed on the grounding base material, and the inner edge and the outer edge are formed at the tip of each protrusion.
Also in this case, it is easy to form the inner edge and the outer edge at appropriate positions, and the smoldering resistance can be ensured and the discharge voltage can be easily reduced.

Further, the distance G1 between the center electrode and the inner edge and the distance G2 between the tip end portion of the shaft hole of the insulator and the outer edge satisfy G2 / G1 ≦ 1.3. Preferred (claim 5).
In this case, spark discharge can be performed between the small-diameter portion and the protruding portion at a lower discharge voltage at normal time when the smoldering is not smoldered.

Further, the radius R3 of the small diameter portion, the radius R4 of the shaft hole, and the axial distance H between the boundary portion and the insulator tip portion satisfy R4-R3 ≧ 0.5 × H. (Claim 6).
In this case, it is possible to prevent a problem that a spark that has splattered at the tip end of the shaft hole of the insulator during smoldering further splatters to the small diameter portion of the center electrode. Thus, during smoldering, it is possible to reliably discharge between the outer edge, the inner wall of the shaft hole of the insulator, and the body portion of the center electrode, and to burn off the carbon adhering to the inner wall of the shaft hole. Therefore, the smoldering resistance can be further improved.
In addition, when R4-R3 <0.5 × H, there is a possibility that the spark that has splattered at the tip of the shaft hole of the insulator at the time of smoldering may be more likely to splatter to the small-diameter part of the center electrode. It may be difficult to improve the performance.

Further, a radial distance R1 from the central axis of the small diameter portion of the central electrode to the inner edge and a radial distance R2 from the central axis of the small diameter portion to the outer edge are 0.1 mm ≦ R2 It is preferable that −R1 ≦ 0.5 mm is satisfied (claim 7).
In this case, sufficient ignitability can be ensured and wear resistance of the protrusions can be ensured.
If R2-R1 <0.1 mm, it may be difficult to ensure sufficient wear resistance of the protrusions. On the other hand, in the case of R2-R1> 0.5 mm, the heat capacity of the protruding portion is increased, which may hinder the growth of flame, and it may be difficult to ensure sufficient ignitability.

Further, it is preferable that the protruding portion protrudes 0.3 mm or more from the grounding base material.
In this case, sufficient ignitability can be ensured.
When the protruding amount of the protruding portion from the grounding base material is less than 0.3 mm, the grounding base material may hinder the growth of flame, and it may be difficult to ensure sufficient ignitability.
Note that if the protrusion amount is too long, the temperature of the protrusion portion becomes high and the protrusion portion may be consumed quickly. Therefore, the protrusion amount is preferably 1.1 mm or less from the viewpoint of suppressing the expansion of the initial spark discharge gap due to wear, that is, suppressing the increase of the discharge voltage.

Further, the body portion of the center electrode may be formed with a step portion that is thinner than the shaft hole and thicker than the narrow diameter portion at the boundary portion.
Also in this case, it is possible to provide a spark plug for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.

Further, the small-diameter portion is made of a noble metal, the cross-sectional area of 0.07～1.13Mm ² by a plane perpendicular to the axial direction, the protruding amount from the boundary portion between the body portion 0.3 The thickness is preferably 1.5 mm (claim 10).
In this case, the wear resistance of the small diameter portion can be obtained, and sufficient ignitability can be ensured.
If the cross-sectional area is less than 0.07 mm ² , it may be difficult to ensure sufficient wear resistance of the small diameter portion. On the other hand, when the cross-sectional area exceeds 1.13 mm ² , the heat capacity of the small-diameter portion is increased, and it may be difficult to ensure excellent ignitability.
Moreover, when the said protrusion amount is less than 0.3 mm, there exists a possibility that it may become difficult for the said trunk | drum to prevent the growth of a flame and to ensure sufficient ignitability. On the other hand, when the protruding amount exceeds 1.5 mm, the temperature of the protruding portion tends to be high, and the wear may be accelerated.

Further, it is preferable that the small-diameter portion of the center electrode is composed of 50% by weight or more of Ir containing at least one additive and having a melting point of 2000 ° C. or more.
In this case, the wear resistance of the small diameter portion can be obtained, and sufficient ignitability can be ensured.

Further, the additive may be composed of at least one selected from Pt, Rh, Ni, W, Pd, Ru, Re, Al, Al ₂ O ₃ , Y, and Y ₂ O _3. Preferred (claim 12).
In this case, a spark plug with a longer life and high reliability can be obtained.

Further, it is preferable that the projecting portion of the ground electrode is made of a noble metal having a melting point of 1500 ° C. or more and containing at least one additive in 50% by weight or more of Pt.
In this case, it is possible to obtain wear resistance of the protruding portion and to ensure sufficient ignitability.

The additive is preferably composed of at least one selected from Ir, Rh, Ni, W, Pd, Ru, and Re (claim 14).
In this case, a spark plug with a longer life and high reliability can be obtained.

In addition, it is preferable that the small-diameter portion of the center electrode has a protrusion amount J from the insulator tip portion of J ≧ 0 (claim 15).
In this case, the ignitability of the spark plug can be ensured.
In the case of J <0, that is, when the small-diameter portion is retracted to the base end side from the insulator tip, the insulator may hinder the growth of the flame kernel, and the ignitability can be ensured. May be difficult.

Example 1
A spark plug for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the spark plug 1 for an internal combustion engine of the present example includes a mounting bracket 2 provided with a mounting screw portion on the outer periphery, and an insulation held by the mounting bracket 2 so that an insulator tip 31 protrudes. An insulator 3, a center electrode 4 held in an axial hole 32 formed in the axial direction of the insulator 3, and a ground electrode 5 that forms a spark discharge gap between the center electrode 4 are provided.

The center electrode 4 includes a body portion 41 inserted into the shaft hole 32 of the insulator 3, and a narrow-diameter portion 42 that is disposed on the distal end side of the body portion 41 and formed narrower than the body portion 41. . Further, the boundary portion 43 between the body portion 41 and the small diameter portion 42 is disposed on the proximal end side with respect to the insulator distal end portion 31.
The ground electrode 5 includes a grounding base material 51 fixed to the mounting bracket 2 and a protrusion 52 that is attached to the grounding base material 51 and is disposed to face the center electrode 4.

The protrusion 52 has an inner edge 521 on the side close to the central axis M of the small diameter portion 42 of the center electrode 4 and an outer edge 522 on the far side.
As shown in FIG. 3, the radial distances from the central axis M of the small diameter portion 42 of the center electrode 4 to the inner edge 521 and the outer edge 522 are R1 and R2, respectively, the radius of the small diameter portion R3 is the shaft hole 32, and If the radius of R4 is R4,
0.7 × R3 ≦ R1 and 0.5 × R4 ≦ R2 ≦ 1.2 × R4 are satisfied.

The distance between the center electrode 4 and the inner edge 521 is G1, the distance between the tip 321 of the shaft hole 32 of the insulator 3 and the outer edge 522 is G2, and the small-diameter portion 42 of the center electrode 4 is grounded. When the axial distance between the protruding portion 52 of the electrode 5 is L and the axial distance between the boundary line 43 and the insulator tip portion 31 is H,
L ≦ G1 ≦ 1.2 × L, G2 + H> G1, and G2 / G1 ≦ 1.5 are satisfied.

In this example, the protrusion 52 is formed on the entire circumference (angle range of 360 °) around the central axis M of the small diameter portion 42.
As shown in FIG. 2, the protrusion 52 has a ring shape, the inner edge 521 is formed on the inner peripheral side of the ring shape, and the outer edge 522 is formed on the outer peripheral side of the ring shape. .

The protrusion 52 is formed by concentrically forming an inner edge 521 and an outer edge 522 around the central axis M.
In this example, the central axis M of the small diameter portion 42 coincides with the central axis of the body portion 41 of the center electrode 4 and also coincides with the central axis of the protruding portion 52.

Further, the inner edge 521 and the outer edge 522 are formed at positions satisfying 0.7 × R3 ≦ R2 and 0.5 × R4 ≦ R1 ≦ 1.2 × R4.
Also, the distance G1 between the center electrode 4 and the inner edge 521 and the distance G2 between the tip 321 of the shaft hole 32 of the insulator 3 and the outer edge 522 satisfy G2 / G1 ≦ 1.3.
Further, the radius R3 of the small diameter portion 42, the radius R4 of the shaft hole 32, and the axial distance H between the boundary portion 43 and the insulator tip portion 31 are R4−R3 ≧ 0.5 × H. Meet.
Further, the radial distance R1 from the central axis M of the small diameter portion 42 of the center electrode 4 to the inner edge 521 and the radial distance R2 from the central axis M of the small diameter portion 42 to the outer edge 522 are 0.1 mm. ≦ R2−R1 ≦ 0.5 mm is satisfied.

The protrusion 52 protrudes from the grounding base material 51 by 0.3 mm or more.
The small-diameter portion 42 is made of a noble metal, has a cross-sectional area of 0.07 to 1.13 mm ² by a plane orthogonal to the axial direction, and a protrusion amount K from the boundary portion 43 with the body portion 41 is 0.3 to 0.3. 1.5 mm.
Further, the small-diameter portion 42 of the center electrode 4 has a protruding amount J from the insulator tip portion 31 such that J ≧ 0. That is, the narrow diameter portion 42 protrudes from the insulator tip portion 31 toward the tip end side in the axial direction.

The small-diameter portion 42 of the center electrode 4 is formed by containing at least one additive in 50% by weight or more of Ir and having a melting point of 2000 ° C. or more. The additive is at least one selected from Pt, Rh, Ni, W, Pd, Ru, Re, Al, Al ₂ O ₃ , Y, and Y ₂ O ₃ .

Further, the protruding portion 52 of the ground electrode 5 is made of a noble metal having a melting point of 1500 ° C. or higher and containing at least one additive in 50% by weight or more of Pt. The additive comprises at least one selected from Ir, Rh, Ni, W, Pd, Ru, and Re.
The small diameter portion 42 and the protruding portion 52 are welded to the trunk portion 41 and the grounding base material 51, respectively.
The insulator 3 is made of a ceramic such as alumina (Al ₂ O ₃ ).

Next, the function and effect of this example will be described.
The protrusion 52 of the ground electrode 5 has an inner edge 521 and an outer edge 522. Therefore, during non-smoldering, it is easy to discharge between the inner edge 521 and the small diameter portion 42 as indicated by reference numeral S1 in FIG. 4, and during smoldering, as indicated by reference numeral S2 in FIG. It becomes easy to discharge via the insulator front-end | tip part 31 between the edge 522 and the trunk | drum 41. FIG.

  In other words, the inner edge 521 can be brought closer to the small diameter portion 42 of the center electrode 4, and the outer edge 522 can be brought closer to the tip 321 of the shaft hole 32 of the insulator 3. Thereby, at the time of non-smoldering, it becomes easy to discharge between the inner edge 521 and the small diameter portion 42 as shown by reference numeral S1 in FIG. 4, and the discharge voltage can be reduced. During smoldering, it becomes easy to discharge between the outer edge 522, the inner wall 322 of the shaft hole 32 of the insulator 3, and the body 41 of the center electrode 4, as indicated by reference numeral S 2 in FIG. As a result, the carbon adhering to the inner wall 322 of the shaft hole 32 can be easily burned out, and the smoldering resistance can be improved.

  The radial distance R1 from the central axis M of the small diameter portion 42 of the center electrode 4 to the inner edge 521 and the radius R3 of the small diameter portion 42 satisfy 0.7 × R3 ≦ R1. Further, a distance G1 between the center electrode 4 and the inner edge 521 and an axial distance L between the small diameter portion 42 of the center electrode 4 and the protruding portion 52 of the ground electrode 5 are L ≦ G1 ≦ 1. Satisfy 2 × L. Therefore, the space between the inner edge 51 and the edge 421 of the small diameter portion 42 can be made close, and the discharge voltage can be kept low.

  Further, the radial distance R2 from the central axis M of the small diameter portion 42 of the center electrode 4 to the outer edge 522 and the radius R4 of the shaft hole 42 are 0.5 × R4 ≦ R2 ≦ 1.2 × R4. Fulfill. Therefore, at the time of smoldering, it becomes easy to cause a spark discharge between the outer edge 521 of the projecting portion 52 and the shaft hole 32 of the insulator 3, and smoldering resistance can be ensured.

  Further, the distance G1 between the center electrode 4 and the inner edge 521, the distance G2 between the tip portion 321 of the shaft hole 32 of the insulator 3 and the outer edge 522, the boundary line 43 and the insulator tip portion 31 The axial distance H between them satisfies G2 + H> G1 and G2 / G1 ≦ 1.5. Therefore, spark discharge can be performed at a low discharge voltage between the small-diameter portion 42 and the protruding portion 52 at the normal time when the smoldering is not smoldered.

  Further, the protruding portion 52 is formed in a 360 ° angular region around the central axis M of the small-diameter portion 42, that is, the entire circumference. Therefore, the carbon adhering to the insulator 3 can be burned out over a wide range, and the smoldering resistance can be sufficiently secured.

Further, a radial distance R1 from the central axis M to the inner edge 521, a radial distance R2 from the central axis M to the outer edge 522, a radius R3 of the small diameter portion 42, and a radius R4 of the shaft hole 32 are:
0.7 × R3 ≦ R2, 0.5 × R4 ≦ R1 ≦ 1.2 × R4,
Therefore, at the time of smoldering, it becomes easy to generate a spark discharge between the inner edge 521 and the insulator 3 and smoldering resistance can be further improved. Further, when not smoldering, it becomes easy to perform a spark discharge between the outer edge 521 and the small diameter portion 42, and the discharge voltage can be reduced and the ignitability can be improved.

  Moreover, since the protrusion part 52 has a ring shape, the inner edge 521 is formed on the inner peripheral side of the ring shape, and the outer edge 522 is formed on the outer peripheral side of the ring shape, the inner edge 521 and the outer edge are formed. It becomes easy to form 522 in an appropriate position in a wide range. Therefore, it is possible to easily ensure smoldering resistance and reduce the discharge voltage.

  Also, the distance G1 between the center electrode 4 and the inner edge 521 and the distance G2 between the tip 321 of the shaft hole 32 of the insulator 3 and the outer edge 522 satisfy G2 / G1 ≦ 1.3. Therefore, spark discharge can be performed between the narrow-diameter portion 42 and the protruding portion 52 at a lower discharge voltage at normal time when the smoldering is not smoldering.

Further, the radius R3 of the small diameter portion 42, the radius R4 of the shaft hole 32, and the axial distance H between the boundary portion 43 and the insulator tip portion 31 satisfy R4-R3 ≧ 0.5 × H. Therefore, at the time of smoldering, as indicated by reference numeral S3 in FIG. it can.
As a result, during smoldering, as shown by symbol S2 in FIG. 4, the discharge is reliably performed between the outer edge 522 and the inner wall 322 of the shaft hole 32 of the insulator 3 and the body portion 41 of the center electrode 4. The carbon adhering to the inner wall 322 of the hole 32 can be burned off. Therefore, the smoldering resistance can be further improved.

The radial distance R1 from the central axis M to the inner edge 521 and the radial distance R2 from the central axis M to the outer edge 522 are 0.1 mm ≦ R2−R1 ≦ 0.5 mm. Fulfill. Therefore, sufficient ignitability can be ensured and wear resistance of the protrusion 52 can be ensured.
Moreover, since the protrusion part 52 protrudes 0.3 mm or more from the grounding base material 51, sufficient ignitability can be ensured.
Moreover, since the protrusion amount J from the insulator front-end | tip part 31 is J> = 0, the small diameter part 42 can ensure the ignitability of the spark plug 1. FIG.

The small-diameter portion 42 is made of a noble metal, has a cross-sectional area of 0.07 to 1.13 mm ² by a plane orthogonal to the axial direction, and a protrusion amount from the boundary portion 43 is 0.3 to 1.5 mm. . Therefore, it is possible to obtain wear resistance of the small diameter portion 42 and to ensure sufficient ignitability.
The small diameter portion 42 is at least 50% by weight of Ir, selected from Pt, Rh, Ni, W, Pd, Ru, Re, Al, Al ₂ O ₃ , Y, and Y ₂ O _3. It contains one type of additive and has a melting point of 2000 ° C. or higher. Therefore, it is possible to obtain the long-life and highly-reliable spark plug 1 capable of obtaining the wear resistance of the narrow-diameter portion 42 and ensuring sufficient ignitability.

  The protruding portion 52 of the ground electrode 5 contains 50 wt% or more of Pt and an additive composed of at least one selected from Ir, Rh, Ni, W, Pd, Ru, and Re. It is made of a noble metal having a melting point of 1500 ° C. or higher. Therefore, the wear resistance of the protruding portion 52 can be obtained, and sufficient ignitability can be ensured, so that the spark plug 1 having a long life and high reliability can be obtained.

  As described above, according to this example, it is possible to provide a spark plug for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.

(Example 2)
In this example, as shown in FIG. 6, the body portion 41 of the center electrode 4 is formed with a step portion 44 that is thinner than the shaft hole 32 of the insulator 3 and thicker than the narrow diameter portion 42 at the boundary portion 43. It is an example of the spark plug 1 for engines.
That is, the radius R5 of the stepped portion 44, the radius R4 of the shaft hole 32, and the radius R3 of the small diameter portion 42 have a relationship of R3 <R5 <R4.

Moreover, the width | variety (namely, R4-R5) of the clearance gap 11 between the step part 44 and the inner wall 322 of the axial hole 32 is about 0.1-0.2 mm, for example.
In this case, a boundary portion between the step portion 44 and the small diameter portion 42 becomes a boundary portion 43 between the body portion 41 and the small diameter portion 42.
Others are the same as in the first embodiment.

In the case of this example, during smoldering, the discharge spark that has struck from the outer edge 521 of the protrusion 52 of the ground electrode 5 to the tip 321 of the shaft hole 32 of the insulator 3 is stepped from the inner wall 322 of the shaft hole 32. It becomes easy to fly to 44. Therefore, although it is difficult for the discharge sparks to fly on the inner wall 322 in the gap 11, the gap 11 is narrow, so that carbon is difficult to deposit here.
Therefore, if the inner wall 322 on the tip side of the step portion 44 can be purified, smoldering resistance can be sufficiently secured.
Therefore, also in the case of this example, it is possible to provide the spark plug 1 for an internal combustion engine that can reduce the discharge voltage while ensuring excellent smoldering resistance.
In addition, the same effects as those of the first embodiment are obtained.

(Example 3)
In this example, as shown in FIG. 7, the protruding portion 52 is not provided on the entire circumference of the central axis M of the small diameter portion 42.
That is, the protrusion 52 has a shape in which a ring shape similar to the ring shape of the protrusion 52 shown in the first embodiment is partially cut, and the formation angle region α around the central axis M of the small diameter portion 42 is , About 260 °. In addition, this formation angle area | region (alpha) needs to be 120 degrees or more.
Others are the same as in the first embodiment.

Also in the case of this example, it is possible to provide a spark plug 1 for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.
That is, since the formation angle region α of the protrusion 52 is 120 ° or more, the spark discharge can be sufficiently performed on a sufficient range of the inner wall 322 of the shaft hole 32 of the insulator 3 at the time of smoldering. Therefore, even if the protrusions are not necessarily provided on the entire circumference of the central axis M of the small diameter portion 42, the smoldering resistance can be sufficiently secured (see Example 11).
In addition, the same effects as those of the first embodiment are obtained.

Example 4
In this example, as shown in FIG. 8, the protrusion 52 is not provided on the entire circumference of the central axis M of the small-diameter portion 42, but is divided into two portions.
That is, the protrusion 52 has a shape that partially leaves two distant portions out of the ring shape similar to the ring shape of the protrusion 52 shown in the first embodiment, and the central axis M of the small diameter portion 42. The total formation angle region 2β around is about 160 °. The formation angle region 2β needs to be 120 ° or more.
The two protrusions 52 are formed at positions that are point-symmetric with respect to the central axis M of the small diameter portion 42.
Others are the same as in the first embodiment.

Also in the case of this example, it is possible to provide a spark plug 1 for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance. Further, by forming the two projecting portions 52 at positions symmetrical with respect to the central axis M of the small diameter portion 42, spark discharge can be performed over a wider range in the inner wall 322 of the shaft hole 32. Can be made. Therefore, the smoldering resistance can be further improved by providing the protruding portion 52 separately.
In addition, the same effects as those of the first embodiment are obtained.

(Example 5)
In this example, as shown in FIG. 9, the protrusion 52 of the ground electrode 5 is changed to various shapes.
That is, the protrusion 52 shown in FIG. 9A has a bottomed cylindrical shape, and a bottomed hole 523 is formed in the center portion. An inner edge 521 is formed at the opening of the bottomed hole 523.

9B has a square outer edge 522 and a bottomed hole 523 having a circular shape in a plan view and a parabolic shape in a longitudinal section. In addition, the bottom portion has an extending portion 524 that protrudes outward from the outer edge 522.
9C has an outer edge 522 that has a trapezoidal shape in vertical section and a circular shape in plan view. Further, the bottomed hole 523 has a square shape in plan view and a triangular shape in the longitudinal section, and an inner edge 521 is formed in a square-shaped opening of the bottomed hole 523.

9D, the outer edge 522 has an oval shape, and the inner edge 521 has a circular shape in plan view. The bottomed hole 523 is formed at a position shifted from the center of the protruding portion 52.
In the protrusion 52 shown in FIGS. 9A to 9D, the depth N of the bottomed hole 523 can be about 0.1 to 0.5 mm.
Others are the same as in the first embodiment.

Also in the case of this example, it is possible to provide a spark plug 1 for an internal combustion engine that can reduce discharge voltage while ensuring excellent smoldering resistance.
In addition, the same effects as those of the first embodiment are obtained.

(Example 6)
In this example, as shown in FIGS. 10 to 12, two protrusions 52 are arranged on the grounding base material 51, and an inner edge 521 and an outer edge 522 are formed at the tip of each protrusion 52. It is an example of the spark plug 1.
Each of the protrusions 52 has a cylindrical shape. The pair of protrusions 52 are disposed at positions that are point-symmetric with respect to the central axis M of the small diameter portion 42 of the center electrode 4.

Further, as shown in FIG. 11, when the spark plug 1 is viewed from the axial direction, a portion on the side closer to the central axis M among the two points where the straight line passing through the central axis M intersects the edge of the tip of the protrusion. Becomes the inner edge 521, and the portion far from the central axis M becomes the outer edge 522.
The positions of the inner edge 521 and the outer edge 522 are formed so as to satisfy the same conditions as those described in the first embodiment. For example, the total formation angle region 2β of the protrusions 52 around the central axis M is 120 ° or more.
Others are the same as in the first embodiment.

Also in this example, it is easy to form the inner edge 521 and the outer edge 522 at appropriate positions, and it is possible to easily ensure smoldering resistance and reduce the discharge voltage.
In addition, the same effects as those of the first embodiment are obtained.
In this example, a cylindrical shape is shown as the shape of the protruding portion 52. However, the protruding portion 52 can be formed in, for example, a quadrangular prism, a triangular prism, or other various shapes.

(Example 7)
In this example, as shown in FIG. 13, two grounding base materials 51 are provided, and one protrusion 52 is provided on each of the two grounding base materials 51.
The grounding base material 51 has a base end portion fixed to a pair of diagonal positions at the distal end portion of the mounting bracket 2, and the other end opposed to the center axis M of the small diameter portion 42 of the center electrode 4. ing.
Others are the same as in Example 6.

Also in this example, it is easy to form the inner edge 521 and the outer edge 522 at appropriate positions, and it is possible to easily ensure smoldering resistance and reduce the discharge voltage.
In addition, the same effects as those of the sixth embodiment are obtained.

(Example 8)
In this example, as shown in FIG. 14, in the spark plug 1 shown in Example 1, the relationship between the radial distance R1 from the central axis M to the inner edge 521 and the discharge voltage of the spark plug 1 was examined. It is.
First, a spark plug 1 having various dimensions in Example 1 as described below was prepared. That is, R2 = 2.0 mm, R3 = 0.3 mm, R4 = 1.2 mm, H = 1.0 mm, and J = 0.2 mm. For L, three types of 0.5 mm, 1.0 mm, and 1.5 mm were prepared.

And the discharge voltage Vs when the dimension of R1 was changed was measured. Further, a spark plug was prepared in which the shape of the protruding portion was the same cylindrical shape as that of the conventional one and the other dimensions were the same as described above, and the discharge voltage Vf was measured.
The reduction rate of the discharge voltage Vs of the spark plug 1 of the present invention with respect to the discharge voltage Vf of the conventional spark plug was obtained by the following formula 1, and the result was plotted in FIG. In the figure, the result when L = 0.5 mm is indicated by ◯, the result when L = 1.0 mm is indicated by □, and the result when L = 1.5 mm is indicated by Δ.
Reduction rate (%) = {(Vs−Vf) / Vf} × 100 (Expression 1)

As can be seen from FIG. 14A, the discharge voltage can be reduced when 0.7 × R3 ≦ R1.
In the spark plug 1 used as the sample of this example, the relationship between the distance R1 and the distance G1 is as shown in FIG. 14B for L = 0.5 mm, 1.0 mm, and 1.5 mm. Have the relationship shown. As can be seen from FIG. 14B and FIG. 14A described above, in the spark plug 1 in which L is 1.5 mm or less, the discharge voltage is reduced in the range of L ≦ G1 ≦ 1.2 × L. ing.

Example 9
In this example, as shown in FIGS. 15 and 16, in the spark plug 1 shown in the first embodiment, the radial distance R2 from the central axis M to the outer edge 522 and the inner wall 322 of the shaft hole 32 of the insulator 3 are shown. It is the example which investigated the relationship with the frequency of flying fire.
In this example, in order to confirm the effect of the position of the outer edge 522, as shown in FIG. 16, a spark plug provided with a protruding portion 52 not provided with an inner edge (see reference numeral 521 in FIG. 3) is used. It was. And the dimension of each part was taken as R3 = 0.3mm, R4 = 1.2mm, H = 1.0mm, J = 0.2mm, L = 1.0mm.

In this spark plug, R2 is changed variously. Then, carbon was attached to the insulator tip 31 and the inner wall 322 of the insulator 3 in each spark plug in advance to form a so-called smoldering state, and then the rate of increase in the number of sparks on the inner wall 322 was measured. The results are plotted in FIG. The rate of increase in the number of sparks is as follows when the number of sparks per unit time when N2 is sufficiently larger than R2 = 2.0 mm and R4, and the number of sparks per unit time of the spark plug to be evaluated is Ns: It is represented by the following formula 2.
Rate of increase in the number of sparks (%) = {(Ns−Nf) / Nf} × 100 (Expression 2)
As can be seen from FIG. 15, the frequency of fire to the inner wall 322 of the shaft hole 32 of the insulator 3 increases in the range of 0.5 × R4 ≦ R2 ≦ 1.2 × R4. That is, smoldering resistance can be improved by maintaining the above range.

(Example 10)
In this example, as shown in FIG. 17, in the spark plug 1 shown in the first embodiment, the ratio G2 / G1 between the distance G2 and the distance G1, and the insulation resistance value between the center electrode 4 and the ground electrode 5 This is an example of examining the relationship.
In this example, the ratio G2 / G1 was changed by changing G1 to a constant value of G2 = 1.2 mm. Specifically, the value of G1 was changed by changing the protrusion amount K of the small diameter portion 42 of the center electrode 4.

Other dimensions were R1 = 0.3 mm, R2 = 1.2 mm, R3 = 0.3 mm, R4 = 1.2 mm, and H = 1.0 mm.
And after changing G2 / G1 and using each spark plug 1 for 5 cycles of the low temperature smoldering fouling test prescribed | regulated to JIS-D-1606, between the center electrode 4 and the ground electrode 5 Insulation resistance was measured. The measurement results are shown in FIG.

  As can be seen from the figure, the insulation resistance increases when G2 / G1 ≦ 1.5, and the effect is large when G2 / G1 ≦ 1.3. That is, by setting G2 / G1 ≦ 1.5, smoldering resistance can be improved, and by setting G2 / G1 ≦ 1.3, excellent smoldering resistance can be ensured.

(Example 11)
In this example, as shown in FIG. 18, in the spark plug 1 shown in Example 3 (FIG. 7), the formation angle region α of the protrusion 52 around the central axis M of the small diameter portion 42 and the center electrode 4 This is an example in which the relationship between the insulation resistance value and the ground electrode 5 is examined.
That is, for each spark plug in which the formation angle region α (FIG. 7) of the protrusion 52 is variously changed, a low temperature smoldering fouling test similar to the above is performed for 5 cycles, and then between the center electrode 4 and the ground electrode 5. The insulation resistance of was measured. The measurement results are shown in FIG.

The dimensions of the other parts of the spark plug are as follows: R1 = 0.6 mm, R2 = 1.4 mm, R3 = 0.3 mm, R4 = 1.2 mm, H = 0.6 mm, J = 0.2 mm, L = 1.0 mm.
As can be seen from FIG. 18, when α ≧ 120 °, the insulation resistance increases, and the effect of suppressing smoldering can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of the vicinity of a tip portion of a spark plug for an internal combustion engine in Embodiment 1; The top view of the protrusion part in Example 1. FIG. FIG. 3 is an explanatory diagram showing a dimensional relationship near the tip of the spark plug in the first embodiment. Explanatory drawing explaining the method of the spark discharge in Example 1. FIG. Explanatory drawing explaining the undesirable spark discharge in Example 1. FIG. Explanatory drawing of the tip part vicinity of the spark plug for internal combustion engines in Example 2. FIG. The top view of the protrusion part in Example 3. FIG. The top view of the protrusion part in Example 4. FIG. Sectional drawing and the top view of the protrusion part of various shapes in Example 5. FIG. Explanatory drawing of the tip part vicinity of the spark plug for internal combustion engines in Example 6. FIG. The top view of the protrusion part in Example 6. FIG. Explanatory drawing which shows the dimensional relationship of the front-end | tip part vicinity of a spark plug in Example 6. FIG. FIG. 9 is an explanatory view of the vicinity of the tip of a spark plug for an internal combustion engine in a seventh embodiment. In Example 8, (A) a measurement result, (B) The diagram which shows the relationship between R1 and G1, respectively. FIG. 10 is a diagram showing measurement results in Example 9. Explanatory drawing of the spark plug used for the test in Example 9. FIG. FIG. 11 is a diagram showing measurement results in Example 10. The diagram which shows the measurement result in Example 11. Explanatory drawing near the front-end | tip part of the spark plug for internal combustion engines in a prior art example. Explanatory drawing near the front-end | tip part of the spark plug for internal combustion engines in a prior art example. Explanatory drawing near the front-end | tip part of the spark plug for internal combustion engines in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Mounting bracket 21 Mounting screw part 3 Insulator 31 Insulator tip part 32 Shaft hole 321 Tip part 322 Inner wall 4 Center electrode 41 Body part 42 Small diameter part 43 Boundary part 5 Ground electrode 51 Grounding base material 52 Projection part 521 Inner edge 522 Outer edge

Claims (15)

A mounting bracket provided with a mounting screw portion on the outer periphery, an insulator held by the mounting bracket so that the tip of the insulator protrudes, and a center electrode held in a shaft hole formed in the axial direction of the insulator And a spark plug for an internal combustion engine comprising a ground electrode that forms a spark discharge gap with the center electrode,
The center electrode has a trunk portion inserted into the shaft hole of the insulator, and a narrow-diameter portion disposed on the distal end side of the trunk portion and formed narrower than the trunk portion. The boundary part with the small diameter part is arranged on the base end side from the insulator tip part,
The ground electrode has a grounding base material fixed to the mounting bracket, and a protrusion that is attached to the grounding base material and disposed to face the center electrode,
The protrusion has an inner edge on the side close to the central axis of the small diameter portion of the center electrode and an outer edge on the far side.
When the radial distance from the central axis of the small diameter portion of the central electrode to the inner edge and the outer edge is R1, R2, the radius of the small diameter portion is R3, and the radius of the shaft hole is R4,
Satisfy 0.7 × R3 ≦ R1, 0.5 × R4 ≦ R2 ≦ 1.2 × R4,
G1 is the distance between the center electrode and the inner edge, G2 is the distance between the tip of the shaft hole of the insulator and the outer edge, and the small diameter portion of the center electrode and the ground electrode When the axial distance between the protrusions is L, and the axial distance between the boundary line and the insulator tip is H,
L ≦ G1 ≦ 1.2 × L, G2 + H> G1, G2 / G1 ≦ 1.5 are satisfied,
The spark plug for an internal combustion engine, wherein the protruding portion is formed in an angle region of 120 ° or more around the central axis of the small diameter portion. 2. The radial distance R <b> 1 from the central axis of the small-diameter portion of the central electrode to the inner edge, the radial distance R <b> 2 from the central axis of the small-diameter portion to the outer edge of the central electrode, The radius R3 and the radius R4 of the shaft hole are
A spark plug for an internal combustion engine, wherein 0.7 × R3 ≦ R2 and 0.5 × R4 ≦ R1 ≦ 1.2 × R4 are satisfied.   3. The protrusion according to claim 1, wherein the protrusion has a ring shape, the inner edge is formed on the inner peripheral side of the ring shape, and the outer edge is formed on the outer peripheral side of the ring shape. A spark plug for an internal combustion engine.   In Claim 1 or 2, the said protrusion part is arrange | positioned 2 or more by the said grounding base material, The said inner edge and the said outer edge are formed in the front-end | tip part of each protrusion part, It is characterized by the above-mentioned. Spark plug for internal combustion engines.   5. The distance G <b> 1 between the center electrode and the inner edge and the distance G <b> 2 between the tip end portion of the shaft hole of the insulator and the outer edge according to claim 1, are: G <b> 2. /G1≦1.3 is satisfied, A spark plug for an internal combustion engine.   In any one of Claims 1-5, the radius R3 of the said small diameter part, the radius R4 of the said axial hole, and the axial direction distance H between the said boundary part and the said insulator front-end | tip part are R4-. A spark plug for an internal combustion engine characterized by satisfying R3 ≧ 0.5 × H.   7. The radial direction distance R <b> 1 from the central axis of the small diameter portion of the central electrode to the inner edge and the radial direction from the central axis of the small diameter portion to the outer edge according to claim 1. A spark plug for an internal combustion engine, wherein the distance R2 satisfies 0.1 mm ≦ R2−R1 ≦ 0.5 mm.   The spark plug for an internal combustion engine according to any one of claims 1 to 7, wherein the protruding portion protrudes 0.3 mm or more from the grounding base material.   In any 1 paragraph of Claims 1-8, The above-mentioned barrel part of the above-mentioned center electrode forms a step part thinner than the above-mentioned axial hole, and thicker than the above-mentioned narrow-diameter part in the above-mentioned boundary part. A spark plug for an internal combustion engine. 10. The thin-diameter portion according to claim 1, wherein the small-diameter portion is made of a noble metal, has a cross-sectional area of 0.07 to 1.13 mm ² by a plane orthogonal to the axial direction, and the boundary with the trunk portion. A spark plug for an internal combustion engine, wherein the amount of protrusion from the portion is 0.3 to 1.5 mm.   11. The internal combustion engine according to claim 10, wherein the small-diameter portion of the center electrode is formed by containing at least one additive in 50% by weight or more of Ir and having a melting point of 2000 ° C. or more. Spark plug for engines. In claim 11, the additive made of at least one selected Pt, Rh, Ni, W, Pd, Ru, Re, Al, Al 2 O 3, Y, from a Y ₂ O ₃ A spark plug for an internal combustion engine.   13. The protrusion of the ground electrode according to claim 10, wherein the protruding portion of the ground electrode contains at least one additive in 50 wt% or more of Pt and has a melting point of 1500 ° C. or more. A spark plug for an internal combustion engine.   14. The spark plug for an internal combustion engine according to claim 13, wherein the additive is at least one selected from Ir, Rh, Ni, W, Pd, Ru, and Re.   15. The spark plug for an internal combustion engine according to claim 1, wherein the small-diameter portion of the center electrode has a protruding amount J from the insulator tip portion of J ≧ 0.

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